Observation of the B_s ⁰→ J/ψϕϕ decay

The B_s⁰ → J/ψϕϕ decay is observed in pp collision data corresponding to an integrated luminosity of 3 fb⁻¹ recorded by the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV. This is the first observation of this decay channel, with a statistical significance of 15 standard deviations. The mass of the B_s⁰ meson is measured to be 5367.08 ± 0.38 ± 0.15 MeV/c². The branching fraction ratio ℬ(B_s⁰ → J/ψϕϕ)/ℬ(B_s⁰ → J/ψϕ) is measured to be 0.0115 ± 0.0012_{− 0.0009}^{+ 0.0005}. In both cases, the first uncertainty is statistical and the second is systematic. No evidence for non-resonant B_s⁰ → J/ψϕK⁺K⁻ or B_s⁰ → J/ψK⁺K⁻K⁺K⁻ decays is found.